The present invention relates to radiographic imaging using a radiation solid state detector and more particularly to a radiographic imaging method and a radiographic imaging system capable of making an efficient use of the radiation solid state detector and displaying proper images though pixel defects in the radiation solid state detector increase over time.
A radiographic image detector has been conventionally used in medicine to produce diagnostic images or in industry for nondestructive tests. The radiographic image detector converts radiation that has penetrated a subject into an electric signal to achieve radiographic imaging. The radiation here includes X-ray, alpha ray, beta ray, gamma ray, electron beam, and ultraviolet ray.
The radiographic image detector is exemplified by a radiation solid state detector, i.e., so-called a flat panel detector hereinafter referred to as FPD, which converts radiation into an electric image signal, and an X-ray image tube that converts a radiographic image into a visible image.
There are two types of FPDs: a direct type and an indirect type. The direct type of FPD collects and reads out electron-hole pairs generated by a photoconductive film such as one formed of amorphous selenium in response to incident radiation, as an electric signal. To be brief, the direct type directly converts radiation into an electric signal. The indirect type has a phosphor layer or a scintillator layer formed of a phosphor that emits light or fluoresces in response to incident radiation to convert radiation into visible light through that phosphor layer, reading out the visible light with a photoelectric transducer. Briefly, the indirect type converts radiation into visible light and the visible light into an electric signal.
One of the causes for image degradation of radiographic images produced by a radiographic imaging system using the FPD is pixel defects of the FPD.
All of the pixels or detecting elements of the FPD do not necessarily produce an output signal with a proper intensity in relation to the amount of incident radiation: some pixels produce an output signal with an abnormally low intensity or an abnormally high intensity in relation to the incident radiation.
Naturally, areas having pixel defects fail to produce proper radiographic image. An image containing such defective areas may cause serious problems such as false or inaccurate diagnoses. In addition, it is impossible to arrest the increase of pixel defects in the FPD that occurs over time.
It is therefore a normal practice with a radiographic imaging system using an FPD to perform pixel detect correction at a given timing whereby the positions of pixel defects of the FPD are detected beforehand at a given timing and, when actually producing a radiographic image, the pixel defects are corrected using data of neighboring pixels according to the pixel defect detection results, so that a radiographic image of which the pixel defects have been corrected may be displayed or printed out by way of reproduction for diagnoses or other purposes.
As the number of pixel defects increases, however, degradation in image quality will necessarily show for all the pixel defect corrections. Notice is therefore preferably given indicating that a given number of pixel defects has been reached or exceeded. Furthermore, it is preferable that the positions where pixel defects are occurring or positions where pixel defects have increased can be correctly recognized to make correct diagnoses or correct interpretation of radiographic images
JP 2000-126162 A discloses a radiographic image processing system that outputs both a radiographic image with corrected pixel defects and a radiographic image with uncorrected pixel defects. JP 2000-132662 A discloses a radiographic image processing system that gives a warning when it is judged upon a pixel defect check that pixel defects have increased or additionally occurred by a number judged to have exceeded a given value. The latter system also displays the positions of pixel defects to enable distinction between pixel defects that have additionally occurred and those that were existent previously thereto.